1. Field of the Invention
The present invention relates to mobile communications. More particularly, the present invention relates to a method and apparatus for scheduling uplink transmissions based on a maximum transmission power and a power headroom reported by a User Equipment (UE).
2. Description of the Related Art
Mobile communication systems have been developed to provide subscribers with voice communication services while on the move using wireless communication services. With the rapid advancement of technologies, the mobile communication systems have evolved to support high speed data communication services as well as the standard voice communication services.
Recently, the next generation mobile communication system of the 3rd Generation Partnership Project (3GPP), Long Term Evolution (LTE) system is being developed. The LTE system realizes high-speed packet-based communication at about 100 Mbps. Regarding commercialization of the LTE system, a discussion is being held regarding two schemes of the LTE system: one scheme for reducing a number of nodes located in a communication path by simplifying a configuration of a network, and another scheme for maximally approximating wireless protocols to wireless channels.
Unlike voice service, in providing data service a resource is allocated according to an amount of data to be transmitted and a channel condition. Accordingly, in the wireless communication system, such as a cellular communication system, a scheduler manages resource allocation in consideration of the resource amount, the channel condition, and the amount of data to be transmitted. This is also the case in the LTE system as one of the next generation mobile communication systems such that the scheduler located in a base station manages and allocates the radio resources used by the LTE system.
Typically, the UE transmits scheduling information to an evolved Node B (eNB) for uplink scheduling in the LTE system. The scheduling information includes a Buffer Status Report (BSR) and a Power Headroom Report (PHR). The PHR is used, when the eNB assigns resources the UE, to limit the transmit power of the UE to a maxim transmission power. If the PHR is not accurate, it is difficult for the eNB to assign and schedule resources effectively and the inaccurate PHR may cause interference with other transmissions and thus it is beneficial for the eNB to have the ability to precisely interpret the PHR reported by the UE.